How do i tell which rooster is older?

We got 6 chicken's recently, 2 roosters and 4 hens. we realized early that one rooster was gonna have to be dinner, but which one? I was told to get rid of the older one, but have no idea which one is older, is it the most aggressive one? or is the weaker one getting too old? How does a person find out?

One way to tell if a rooster is young or old is by looking at their legs. If the scales are very smooth, that is young. If the scales look sort of thick and not so smooth.. it's probably older(need to make distinction between normal older legs vs scaly leg mites though). Also the spur size can help- if the spurs never was filed or cut off or molted, on the older roosters the spurs are an inch long or longer. If there's no spur or just like a little bump, it's a very young one(year old or less).

thank you for your responses they have been very helpfull, we are going to try taking the aggressive rooster out of the coop and letting the weaker one in for a while and see if his legs heal from being pecked.